(1) Field of the Invention
The present invention relates to a protection device for protecting a rotorcraft against a pyramid-shaped structure for carrying a load, to a fastener system provided with said device and with said structure, and to a rotorcraft provided with the fastener system. The invention also relates to a method of use.
The technical field of the invention is thus the field of devices for fastening an external load to an aircraft, and in particular to an aircraft having a rotary wing.
(2) Description of Related Art
Conventionally, a rotorcraft comprises a fuselage carrying at least one rotor for providing it with lift and possibly also with propulsion. The rotorcraft may then be provided with a releasable fastener system for carrying an external load.
Such a fastener system usually includes a release-hook that is optionally swivel-mounted and that is fastened to the fuselage by fastener means. A sling is then attached to the release-hook in order to enable external loads to be carried.
The fastener system may in particular by a system known as a “cargo swing”, or as a “swing” for short.
The swing fastener system may include a pyramid-shaped structure. The pyramid-shaped structure has a frame having a quadrilateral shape and four arms, each arm extending in elevation from the frame up towards an apex.
More precisely, the pyramid-shaped structure possesses a pair of two front arms and a pair of two rear arms. The terms “front” and “rear” are used with reference to the forward direction of the aircraft.
In particular, the pyramid-shaped structure may possess two long arms and two short arms, with the apex then not being placed vertically over the intersection of the diagonals of the frame. For example, the front arms may be the short arms and the rear arms may be the long arms.
The frame may be made using four tubes connected together in pairs, each arm being fastened to one of the corners of the frame, for example. The frame may also be obtained using four independent tubes, each tube extending between two adjacent arms.
The fastener system may also be rigid or hinged.
The four arms may be connected so as to constitute the apex of the fastener system. The four arms are then secured to one another.
Nevertheless, the arms may be connected together in pairs. For example, the two front arms may have their top ends connected together, with the two rear arms also being connected together at their top ends. The top ends of the front and rear arms are then hinged about respective axes of rotation to a baseplate constituting the apex.
The two front arms thus constitute a front assembly that can pivot relative to a rear assembly constituted by the two rear arms.
The tubes constituting the frame of the pyramid-shaped structure are then adapted to accommodate such relative pivoting between the front and rear assemblies.
Independently of the type of fastener system, a release-hook is usually suspended from the apex of the pyramid-shaped structure. Movement of the release-hook within the fastener system is restricted to the zone defined by the frame of the pyramid-shaped structure.
The pyramid-shaped structure is also suspended under the fuselage, e.g. by four suspension cables.
The swing fastener system is in satisfactory use in the field of aviation.
Nevertheless, the pyramid-shaped structure can be dangerous in the event of the rotorcraft crashing.
During a crash, when the landing gear is deformed under the effect of the energy it absorbs, the pyramid-shaped structure comes into contact with the ground. The pyramid-shaped structure then runs the risk of perforating the fuselage, since the pyramid shape of such the structure makes it very strong against collapsing. The forces needed to collapse the pyramid-shaped structure are thus very great. The pyramid-shaped structure thus runs the risk of not collapsing, and thus of striking the fuselage and of perforating it.
The situation becomes even more complicated when a rotorcraft has its fuel tank in the bottom portion of the fuselage that also supports the pyramid-shaped structure.
In the bottom region of the fuselage, the rotorcraft then includes in particular a plate serving for example to receive pumps, level gauges, and other pieces of equipment of the fuel circuit. That plate is designed to withstand contact with the ground in the event of a crash in order to preserve the leaktightness of the tank. Nevertheless, an impact against the apex of a pyramid-shaped structure can be destructive, and the plate runs the risk of not being able to withstand the forces delivered by the pyramid-shaped structure.
Furthermore, even if the pyramid-shaped structure does collapse, metal debris from the pyramid-shaped structure still presents a risk of perforating the tank.
Also known are documents EP 2 481 671, U.S. Pat. Nos. 3,044,818, 5,069,318, 5,344,203, 4,378,919, and WO 95/06585.